Now im mainly speaking PvE Here, But from the Cinematics for World of Warcraft (The Wrath gate is the prime example here)From the cinematic, you can see horde & alliance fight together,they can also communicate together not just "Kek Bur Fus Koi pfjajwlkej"This cinematic was really epic, but saddens me to feel that its pretty much nonsense in reality (by reality I mean in game)

I think that at some point in the future, this Gap becomes obsolete and goes under a number of changes and becomes narrowed.